Method and apparatus for rolling threads



Aug. 24, 1965 F. WALTERS 3,201,964

METHOD AND APPARATUS FOR ROLLING THREADS Filed Jan. 21, 1963 2 Sheets-Sheet 1 INVENTOR. f9??? m/ze m1 Aug. 24, 1965 F. WALTERS 3,201,964

METHOD AND APPARATUS FOR ROLLING THREADS Filed Jan. 21. 1963 2 Sheets-Sheet 2 I N VENTOR.

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United States Patent 3,201364 METHOD AND APPARATUS FOR ROLLING THREADS Fritz Walters, Grosse Pointe Woods, Mich, assignor to Detroit Tap & Tool Qornpany, Warren, Mich a corporation of Delaware Filed Jan. 21, 1963, Ser. No. 252,770 6 Claims, (Cl. 72-198) This invention relates to the art of forming threads and the like, and more particularly to an improved method and improved apparatus for forming threads or teeth on toothed elements.

A variety of methods and apparatus are known for rollforming threads, a common method being that which utilizes a pair of annular die members having threadforming surfaces on the periphery and supported in spaced relationship in a tool holder. A workpiece, for example, such as a threaded fastener in the form of a bolt or a screw, is adapted to be received between the dies and the thread is formed on the workpiece by relative rotation between the dies and the workpiece. The depth and shape of the thread is progressively formed to the finished dimensions by exerting pressure between the workpiece and the dies until the desired depth and shape are attained. Other methods of forming threads include the use of flat dies, one or more of which are moved relative to the workpiece to obtain a comparable thread-forming motion.

In any event, and regardless of the particular type of die or method of obtaining relative motion between the workpiece and the die during thread formation, insofar as is known, all previous thread-forming operations involving displacement of material to form the threads, rather than and as distinguished from a material cutting operation resulting in removal of chips of material, have utilized a method which can be characterized as involving unequal volumetric displacement of material per unit of forming movement between the die means and the workpiece during different portions of the forming operation.

The use of prior art methods and apparatus with which unequal volumes or amounts of material are displaced on the workpiece at different stages of the thread formation inevitably leads to certain disadvantages. One basic disadvantage is that the forming pressure required to displace the material of the workpiece into the proper location for the formation of threads varies at different stages of manufacture, depending upon the amount of material being displaced, the distance through which the material is displaced, etc. Although other factors, such as plasticity of the material, temperature of the material, frictional resistance between the forming tool and the material, etc., may affect the force required to obtain a particular r sult; the present invention enables substantially improved results to be obtained by closely controlling the amount of material displaced during the formation of the threads.

Accordingly, a primary object of the present invention is to provide new and improved methods and apparatus for forming threads and the like on a workpiece.

Another object of the invention is to provide means for forming threads utilizing relatively equal forming pressures during substantially all stages of formation of the threads.

A further object is to provide a method and means for manufacturing threads on a workpiece which result in displacement of substantially equal amounts of material on the workpiece during all stages of manufacture so that the formation of the threads by material displacement is substantially uniform and continuous.

A further object of the invention is to provide a method and apparatus for forming threads by displacement of material on a workpiece whereby the amount of material of the workpieces displaced during various movements between the workpiece and the forming means is substan- .tially equal.

One of the main advantages of utilizing a method and apparatus in accordance with the principles of the present invention is that the wear rate of the dies used for forming the threads is more uniformly spread out over the entire forming cycle and high stress or failure points or areas on the forming dies are thereby reduced with the result that the tendency for portions of the forming surface of the dies to fail prematurely is substantially reduced.

The inventive principles utilized to attain the objects and advantages of the present invention are hereinafter described in detail by reference to the accompanying drawing, wherein:

FIGURE 1 is a side elevational view of a thread-forming die embodying the present invention;

1516. 2 is .a partial cross sectional view of the forming surface of the die of FIGURE 1;

FIG. 3 is a longitudinal sectional view diagrammatically illustrating a series of formed threads.

FIG. 4 is an enlarged partial sectional View of a forming tooth of FIG. 2;

FIG. 5 is a side elevational view, partly in section, showing a forming tooth in forming engagement with a workpiece;

FIG. 6 is a diagrammatic illustration of a workpiece mounted between dies embodying the present invention; and

FIG. 7 is a schematic illustration of another embodiment of the invention.

The inventive principles hereafter disclosed in detail are applicable to the formation of various toothed elements including but not limited to threads, splines, teeth, and the like, which may be characterized as comprising alternate lands and grooves. This invention relates particularly to formation of such lands and grooves by displacement of material from one portion of a workpiece to form the groove and deposition of the displaced material or its equivalent volume of material at another portion of the workpiece to form the lands.

Referring to the drawings, the invention is illustrated in connection with thread-forming means in the form of a roller die it) which, as shown in FIGURE 6, is adapted to be mounted on a spindle in a thread-rolling machine in cooperative relationship with a similar die 19'. A centrally located shaft aperture 12 is provided in the die 10' to facilitate mounting the die on the machine spindle. The periphery of the annular roller die 10 is provided with a working surface defining a series of annular thread-forming teeth 1 16, 18, 2d. The forming die 10 embodying the present invention is illustrated as comprising two oppositely located work surfaces 24 and 26 which are separated by relief areas 28, 30. A workpiece W is initially positioned between a pair of identical roller dies 10 and to, as shown in FIG. 6, in one of the relief areas 28 or trically formed and gradually increased in diameter from a minimum at the leading end to a maximumat a point approximately 100 from the leading end. The depth'of 1 penetration at such point would therefore be at a maximum and equal to the depth (root) of the grooves of the thread being formed. In such prior art dies, the rise, or change in eccentricity, f the forming portionwas substantially constant and gradual so that the depth of penetration of the roller die teeth per unit of rotation of the roller die was substantially equal throughout the length of formed threads'without further penetration. The concentric working surface of the prior dies terminated in a radially inwardly inclined surfa-ce' extending for approximately 7 and provided a substantial radial inward drop to a relief area extending'for approximately 40 to the leading end of the next workingsurface.

Referring now to FIGS. 3 and 4, an analysisof the formation process of threads by use of a prior roller die will showthat for each radial inward unit X-of penedisplacement of the material on the workpiece by radially inward penetration of the teeth on the working surface of the roller dies per unit of relative rotation between the workpiece and the roller dies, the radial depth of penetration must be successively smaller to'cause equal volumetric displacement of material on the workpiece per unit of relative rotation. In other words, 'referring again to FIGURES 3 and 4, if the portions 56-66 of a tooth 16 are forced into the workpiece W successively at each unit of relative rotation a distance equal to .0027 inch, the volumetric displacement of material on the workpiece W would be equal to, successively, the unequal volumes represented by the portion 56 of S units, the portion 58 of 7 units, the portion 60 of 9 units, the portion 62 ,of'll units, the portion 64 of 13 units, and the portion 66 of 15 units.

In order to obtain substantially equal volumetric displacement, in the preferred embodiment of the invention illustrated, the rise along the work surfaceportions of the die is. varied inaccordance with the. progressively larger change in volumetric, displacement occurring during penetration of the teethof the roller. die into the workpiece. Accordingly, the depth of penetration, as controlled by the change in rise in the. work surface 'portion36 for the initial 100 of rotation, is decreased as the teeth onthe roller die progressively form the thread "changethat was directly proportional to volumetric tration of a forming tooth of the roller die, a different unit volume of material must be displaced from the workpiece to accommodatev the penetration of the tool; This is easily seen by comparison ofthe. crosssectional areas, 56, 58, 60, 62, 64 ofthe tooth. By dividing each unit volume representation58-66 into equal triangular areas, it may be seen that the variation involurne ranges from 5 units at .0027 inch penetration to'1 5 units at .0162 inch penetration in the example illustrated wherein it is assumed that a total depth'of penetration of .0162 inch is desired. Accordingly, with previous apparatus utilizing a' gradual uniform rise in the working surface, and, consequently, equal depths of penetration per unit of rotation of a given tooth on the die, varying, gradually "increasing,,volumes of material had to be displacedon variation; However, practically, the rise portions of a 'roller' die Working surface maybe dividedinto segan amount adapted'to adequately compensate for the volumetric variation and produce satisfactory results with a minimum of expense in manufacture.

, the point 33 and including the initial 40 of rotation is desirable, the rise in theinitial 10 of rotation being utilized to, initiate rotation of the workpiece inthe conthe workpiece to accommodate the same degree of angular rotation of the roller dies at later stages of the process as compared with early stages of the process;

In accordance with the'present invention, amethod and apparatus is provided for forming threads by substantially constant volume displacement of material on ventional manner. While an initial penetration of .0077 inch during the first 40 of rotation constitutes approximately.47.5% of the total depth of penetration desired, an examination of FIG. 4 clearly shows'that 33 /a% of the materialis displaced- During the next 30 of rotationfrom the point 33 to the point 34, the workpiece is the workpiece perunit of rotation of the working surface of the forming means. A thread. formed on thelwork piece W and comprising, in cross section, adjacent tooth represent portions of the workpiece displaced to form the grooves 70'and 71. In the final form of the threads, the cross sectional area-of thegroove portions 74 and 76 below the line 72 are substantially equal to tooth portion 68 above 'the line, 72; material of the workpiece, which forms the teeth 67, 68, 69 will be displaced from the groove areas in substantially equal parts outwardly beyond the line 72 to form the tooth portions. 7 is substantially equal to the area of anyone tooth and the volume of material displaced to; form the groove is approximately equal to the volume of material required to form the tooth. In order to obtain equal volumetric As shown schematically, the

penetrated an additional .0046 inch which constitutes 28.4% of the, total depth of penetration and yet 33 /s% of the material is displaced. In the zone extending from the point 34to the point 35,-which also includes 30 of rotation, the workpiece is penetrated anadditional .0039

inch'which constitutes approximately 24.1% of the total depth of penetration, but displaces 33 /s% of the total volume of the workpiece which must be displaced. Thus,

it may be seen that between the points 32 and ,35 the total depth of penetration, is reached with an initial. penetration of approximately 47.5% of the total depth ofpenetration during the first 40 of rotation and with progressively"decreasingamounts of'penetration in each 'of the subsequent portions of the working surface which constitute-28.4% and 24.1%, respectively, of the total depth of penetration and each ofwhich displaces 3 3 /3%. of'the total volume of material displaced.

.If desired, the progressive decrease in penetration as the cross sectional area of the formingteeth increase can be calculated to provide exactly volumetric displacement for any. desired increments, of relative rotation. How- 'ever, as hereinbefore indicated, a relatively broad range -ditions -to be maintained during theproduction of rollformed threads;

As shown in FIGURE 1, the working surface of the die then continues in a concentric portion 37 of maximum diameter for approximately 33, the concentric portion being utilized to finish the formed thread without further penetration. The concentric portion 37 of the working surface terminates in a radially inwardly inclined zone 38 which serves to gradually relieve the pressure between the workpiece and the die and provides a substantial radial inward drop to the relief zone 28 which extends for approximately 40 to the leading end portion of the next working surface 26, the relief zone enabling workpieces to be loaded and unloaded from between the dies.

Since the roller-forming die shown by way of illustration is provided with two working surfaces, it should be understood that the percentages of rise or penetration and the angular degree of working surface provided can be changed to suit various needs and conditions and various types of forming apparatus. Although a presently preferred method of dividing into segments over which varying amounts of depth penetration are attained with a uniform rise to facilitate manufacture has been disclosed, it should also be recognized that the particular degrees of angularity over which the percentage depth penetration is spread can be varied within a large range of working surface lengths depending upon the degree of control desired to be attained.

While a rotary die having two working surfaces has been described herein, it should be understood that the inventive principles herein disclosed are equally applicable to dies having a single continuous working surface, to dies in the form of fiat racks and to thread forming machines having cam operated means to effect movement of concentric dies. For example, dies which have a concentric working surface around substantially the entire periphery thereof and which are adapted for use in threadrolling machines having cam means which is utilized to effect movement of the dies into pressure forming engagement of the workpiece can be utilized to employ the principles of the present invention by providing the cams with surfaces which move the concentric dies to effect a progressive decrease in the rate of penetration of the workpiece as the dies move relative to the workpiece. In FIG. 7, a concentric die 80 is illustrated having teeth 82 which extend around the entire periphery thereof in concentric relationship with respect to the axis 84 of the die 80. The die 80 is shown mounted for rotation about a pin 86 carried by a cam follower 88 which may be mounted in a thread-rolling machine in the conventional manner. The cam follower 88 is biased against a cam 90 by a spring 92, one end of which bears against a shoulder 94 provided on the cam follower 88, while the opposite end of the spring bears against a stop 96 provided on the thread-rolling machine. The cam surface 98 of the cam 00 is provided with a configuration such that an initial penetration of .0077 inch from the leading end 100 of the cam to the point 102 and including the initial 40 of rotation of the cam is effected as the cam moves the cam follower and consequently the concentric die into pressure forming relationship with the workpiece W, the rise in the initial 10 of rotation of the cam being utilized to initiate rotation of the workpiece. While the initial penetration of .0077 inch during the first 40 of rotation of the cam constitute approximately 47.5% of the total depth of penetration desired into the workpiece, only 33 /s% of the metal is displaced. During the next 30 of rotation of the cam from the point 102 to the point 104, the workpiece is penetrated an additional .0046 inch which constitutes 28.4% of the total depth of penetration, but 33 /3% of the material is again displaced. In the zone extending from the point 104 to the point 105 which also includes 30 of rotation of the cam, the cam forces the workpiece to penetrate an additional .0039 inch which constitutes 24.1% of the total depth of penetration and thereby displaces 33 /s% of the total volume of the 6 workpiece which must be displaced. The cam then continues in a concentric portion 108 for approximately 33, the concentric portion being utilized to force the concentric die against the workpiece without further penetration so as to finish form the thread on the workpiece. The concentric portion 108 terminates in the radially inwardly inclined zone 10 which serves to gradually relieve the pressure between the workpiece and the die and serves to withdraw the die gradually from the workpiece. A relief zone 112 is provided which extends for approximately 40 to the leading end of the next Working cam surface, the relief zone enabling workpieces to be loaded and unloaded from the machine.

Accordingly, it is intended that the subjoined claims be constituted to include those alternative embodiments and modifications which incorporate the inventive principles disclosed except insofar as limited by the prior art.

What is claimed is:

l. A rotary die for pressure forming threads comprising a body having an axis of rotation and a Work surface on the periphery thereof, said work surface including an eccentric portion having teeth thereon progressively increasing in diameter, the rate of increase in diameter progressively diminishing whereby the rate of penetration of said teeth on said eccentric portion into the workpiece progressively diminishes so that substantially equal volumes of material are displaced on said workpiece per unit of movement of said teeth on said eccentric portion relative to said workpiece.

2. A rotary die for pressure forming threads comprising a body having an axis of rotation and plurality of work surfaces on the periphery thereof separated by relief areas, said work surfaces each including an eccentric portion having teeth thereon progressively increasing in diameter, the rate of increase in diameter progressively diminishing whereby the rate of penetration of said teeth on said eccentric portion into the workpiece progressively diminshes so that substantially equal volumes of material are displaced on said workpiece per unit of movement of said teeth relative to said workpiece.

3. The method of forming threads which taper from the roots to the crests thereof on a generally cylindrical workpiece, which comprises the steps of rolling said workpiece in engagement with a tool having tapered teeth generally complemental to the teeth to be formed on said workpiece and gradually advancing said tool radially toward said workpiece at a decreasing rate whereby to achieve substantially equal volumetric displacement of material on said workpiece per unit of rolling movement of the workpiece during the tooth forming operation.

4. The method of forming a cylindrical threaded workpiece for threads which have a substantially greater thickness at the roots thereof than at the crests thereof which comprises the steps of rolling said workpiece in engagement with a tool having at least one thread forming tooth generally complemental to the thread to be formed on said workpiece advancing said tool radially toward said workpiece at a gradually decreasing rate whereby substantially equal volumetric displacement of material on the workpiece will be obtained for each unit of rolling movement of said workpiece relative to said tool.

5. In a machine for forming teeth tapered from the roots to the crests thereof on a workpiece including, in combination, a forming tool having a tooth tapered from the root to the crest thereof, and complemental to the teeth to be formed on said workpiece, means for effecting engagement of said tapered tooth of said forming tool and said workpiece so as to apply pressure therebetween, and means controlling the rate of formation of said teeth and the rate of displacement of material on said workpiece so that substantially equal volumes of material on said workpiece are displaced per unit of movement of said tapered tooth relative to said workpiece.

6. In a machine for forming teeth tapered from the roots to the crests thereof on a workpiece including, in

7 8 combination, a rotary forming tool having a tooth thereon I 7 References Cited by the Examiner tapered from the root to the crest thereof, complemental UNITED STATES PATENTS to the teeth to be formed on said workpieceQsaid tapered 71 360 1 7 Bra ton 80 61 tooth adapted to engage a workpiece and displace j 2 183688 12/39 Olsgn f material of Said workpiece to form said threads, means 5 2:983:171 5/61 Laban V mounting said rotary forming tool in engagement with the workpiece so as to apply pressure therebetween, and FOREIGN PATENTS means for forcing said tapered tooth into said workpiece 12 723 3/57 R s i whereby substantially equal volumes of material on said a I workpiece are displaced per unit of movement of said 0 CHARLES LANHAM P r m 'f rotary tool relative to said workpiece. MICHAEL V. BRINDISI, Examiner. V 

1. A ROTARY DIE FOR PRESSURE FORMING THREADS COMPRISING ING A BODY HAVING AN AXIS OF ROTATION AND A WORK SURFACE ON THE PERIPHERY THEREOF, SAID WORK SURFACE INCLUDING AN ECCENTRIC PORTION HAVING TEETH THEREON PROGRESSIVELY INCREASING IN DIAMETEER, THE RATE OF INCREASE IN DIAMETER PROGRESSIVELY DIMINISHING WHEREBY THE RATE OF PENETRATION OF SAID TEETH ON SAID ECCENTRIC PORTION INTO THE WORKPIECE PROGRESSIVELY DIMINISHES SO THAT SUBSTANTIALLY EQUAL VOLUMES OF MATERIAL ARE DISPLACED ON SAID WORKPIECE PER UNIT OF MOVEMENT OF SAID TEETH ON SAID ECCENTRIC PORTION RELATIVE TO SAID WORKPIECE. 